1 John 4:2
1 John 4:22By this you will know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is from God,
Watchtower publications treat 4:2 as a loyalty test in modern dress: the "spirit of truth" is the spirit that produces the Watchtower's doctrine about Jesus, and the "spirit of antichrist" is anything else. In the rs framing of 1 John, "confesses Jesus Christ as having come in the flesh" is read expansively as "accepts the Watchtower's teaching about Jesus" rather than as the historical-critical reading of the Greek (note Irenaeus and Hippolytus reading it against docetism).
Let the verse's own content set the test. John's Greek phrase is specific: "Ἰησοῦν Χριστὸν ἐν σαρκὶ ἐληλυθότα" — Jesus Christ having come (perfect participle) in flesh. The test is not denominational loyalty; it is a Christological test with defined content, aimed at first-century teachers who denied that the Christ-spirit truly took on a fleshly human body. Every mainline Protestant confession — Reformed, Lutheran, Anglican, Methodist, Baptist — confesses Jesus Christ come in the flesh in exactly John's sense. So by John's stated criterion we are on his side of the line. When a JW is tempted to expand the test to "whoever opposes Jehovah's organisation," note gently that once the content is substituted the word stops being a Christological marker and becomes an institutional badge. John's content is narrower than that — and for the Watchtower's own Christology, narrower is the problem.